The problem has been identified on seven engines on five different aircraft. Two of the planes have already returned to service. The other three “will need another few weeks to fix,” ANA spokesperson Ryosei Nomura said.

The gearbox is built by Hamilton Sundstrand, a unit of United Technologies Corp.

ANA was Boeing’s (NYSE: BA) launch customer for the 787 Dreamliner. It is currently one of two operators that are flying the aircraft, the other being Japan Airlines Co. That carrier’s Dreamliners are fitted with engines from General Electric Co.

ANA, which now has 11 Dreamliners, said it canceled two 787 flights over the weekend.